The present invention relates to a rotary projector for a coating material. The present invention also relates to a rotary spraying member for a coating material. Furthermore, the present invention relates to a method for spraying a coating material using such a rotary projector.
Traditional spraying using rotary projectors is used to apply a coating material on objects to be coated, such as motor vehicle bodies. Coating material refers to any material intended to be projected in the form of droplets on an object to be coated, such as a finish, paint or varnish, or a phytosanitary material to be sprayed on plants, etc.
A rotary projector for projecting a coating material includes a spraying member rotating at high speeds under the effect of rotational driving means, such as a compressed air turbine. Such a spraying member generally assumes the form of a bowl with rotational symmetry and it includes at least one spraying edge able to form a jet of coating material. The rotary projector also includes a fixed body housing the rotating means as well as means for supplying the spraying member with coating material.
The jet of coating material sprayed by the edge of the rotary member assumes a generally conical shape that depends on parameters such as the speed of rotation of the bowl and the flow rate of the coating material. To control the shape of the jet, the rotary projectors of the prior art are generally equipped with several orifices. These orifices are formed in the body of the rotary projector, on a circle situated on the outer perimeter of the bowl and centered on the axis of symmetry of the bowl. These orifices are intended to emit jets of air making it possible to shape the jet of coating material.
JP-A-8 071 455 describes such a rotary projector for which the air jets emitted from the outer perimeter of the bowl are intended to reduce the vacuum existing downstream of the bowl and to obtain a uniform deposited film of paint.
However, such a rotary projector induces relatively high air speeds, which risks deteriorating, qualitatively and quantitatively, the application of the coating material on the object to be coated.
Qualitatively on the one hand, an object coated using such a rotary projector has impacts whereof the profiles are sometimes irregular and generally not very robust. The robustness of an impact from a rotary projector of a coating material corresponds substantially to the regularity of a curve showing, as a function of a particular parameter such as the skirt air flow rate, the “impact width,” i.e. the width of the middle or upper deposited thickness area, considered in a direction perpendicular to the direction of the relative movement between the rotary projector and the object to be coated.
Quantitatively on the other hand, the deposition yield of such a rotary projector is relatively limited. The deposition yield, also called transfer efficiency, is the ratio of the quantity of coating material deposited on the object to be coated to the quantity of coating material projected using the rotary projector.
DE-A-10 2007 012 878 discloses a projector in which a flow of air is used to shape a central jet of paint and press a peripheral flow against a flow surface of a bowl. The air injection means situated outside the flow surface of the bowl does not make it possible to act on the robustness of the coating material impact or the deposition yield.
The present invention aims in particular to resolve these drawbacks by proposing a rotary projector for a coating material making it possible to overcome the vacuum downstream of the bowl, obtain a good robustness of the coating material impact on the objects to be coated, and limit dirtying of the components of the bowl.